My daughter is 7 and has made her costume for the last few year. Some year more successfully than others.
At 5 she wanted to be a rock star with her belly showing. When she could explain how the belly showing improved her rock star music, I would agree. I offered other ideas for costumes (looking on line at Martha Stewart and other websites). She shouted, "I'd rather be the kitchen sink." My reply, "That works. How are you going to do that?" She stormed out. An hour later she was back the kitchen with a dishpan filled with toy dishes from her play kitchen. She was dressed in her gray leggings and a gray turtleneck. Calmly she asked me to take her to the Halloween store for gray hairspray and face paint because she was being the kitchen sink. We pulled her hair up on top of her head in a hair tie (elastic thingy), put a piece of cardboard w/ hanger piece taped to it between the hair (some on top and bottom) and held in place with more hair ties (This was the water handle.) and sprayed her hair silver. I applied silver face and hand paint. She carried around her tub of dishes. She also had a water bottle in the tub. She would fill her mouth with water and when someone (teacher) pressed her handle (hair), she spit water into the tub. She was a hit and inspired her classmates to make their own costumes the next year. Our of 20 1st, there were only two store bought costumes last year.
Last year, Captain Underpants (story book character)...boy underwear and a red cape. Yes, my 1st grader wanted to go to school in only underwear and cape. Her teacher was cool with it, but her dad and I weren't. Once I pulled out the flesh colored leotard, she changed her mind and went as Gabriella from High School Musical.
This year, I'm going as Captain Underpants. Yes, I teach at the same school.Hehehehehehe
She is being a vampire and using all of her dress up stuff to create her own costume. We bought fangs and that's it.
If you have time, make it. Have your son help. It's a lot of fun and really lets them be creative.
Stephanie